In an electrical wire bundled portion in which conductors of electrical wires are tied together, for example, a hot-melt resin or the like is used to waterproof and protect the electrical wires. However, there is a concern that the hot-melt resin may melt again when heated to a high temperature, causing slippage to occur in the hot-melt resin.
Accordingly, a pressure-sensitive adhesive sheet for waterproofness and airtightness has been proposed to make up for the drawback of the hot-melt resin (e.g., Japanese Patent No. 4920400). The pressure-sensitive adhesive sheet is composed of a crosslinked solid-type tackifier composition including (a) a rubbery polymer, (b) a tackifier, and (c) a crosslinking agent.